Questions and Answers
Where should you look for more in-depth information on corrosion?
FAA Advisory Circular 43-4B Corrosion Control for Aircraft
What is the 43-4B?
An extensive handbook that deals with the sources of corrosion particular to aircraft structures.
How does corrosion appear on the surface of aluminum alloys and magnesium?
It appears as pitting and etching and is often combined with a gray or white powdery deposit.
What are the two general classifications of corrosion that cover most of the specific forms?
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In corrosion, what does the metal change into?
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What are the two simultaneous changes involved in the corrosion process?
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What is Direct Chemical Attack?
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What are the most common agents causing direct chemical attacks?
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What are the four conditions for Electrochemical Attack?
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What factors of the metal determine the form of corrosion?
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What does surface corrosion appear as?
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What may result from dissimilar metal contact in the presence of a conductor?
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Dissimilar metal is in what class of corrosion?
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Why is dissimilar metal corrosion serious?
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What can the improper use of steel cleaning products cause?
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What is Intergranular Corrosion?
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Aluminum alloys and some steels are susceptible to what type of electrochemical corrosion?
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What is Exfoliation Corrosion?
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What is Fretting Corrosion?
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What characterizes fretting corrosion?
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What are some preventive maintenance strategies for corrosion resistance?
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What specific functions are included in corrosion PM?
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Study Notes
Corrosion Control and Cleaning in Aviation
- Refer to FAA Advisory Circular 43-4B for comprehensive corrosion information related to aircraft.
- 43-4B is an extensive handbook specifically addressing corrosion sources affecting aircraft structures.
Appearance and Classification of Corrosion
- Aluminum alloys and magnesium exhibit corrosion as pitting and etching, often accompanied by a gray or white powdery residue.
- Corrosion primarily falls into two classifications: direct chemical attack and electrochemical attack.
Corrosion Process and Chemical Composition
- Corrosion converts metal into metallic compounds like oxides, hydroxides, or sulfates.
- The corrosion process involves:
- Anodic change where the metal is oxidized.
- Cathodic change where the corrosive agent is reduced.
Direct Chemical Attack
- Occurs due to direct exposure of bare surfaces to caustic liquids or gases.
- Common agents include spilled battery acid, battery fumes, residual flux deposits, and trapped caustic cleaning solutions.
Conditions for Electrochemical Attack
- Four conditions must be present:
- A metal undergoing corrosion (anode).
- A dissimilar conductive material (cathode) that corrodes less easily.
- A continuous conductive liquid path (electrolyte).
- Electrical contact between anode and cathode, often via rivets, bolts, or corrosion.
Factors Affecting Corrosion Form
- The specific form of corrosion is influenced by:
- The type of metal involved.
- Size and shape of the metal.
- Specific functional use.
- Atmospheric conditions.
- Present corrosion agents.
Types of Corrosion and Their Implications
- Surface corrosion manifests as roughening, etching, and pitting, frequently with a powdery deposit.
- Dissimilar metal contact with a conductor can cause severe pitting damage.
- Dissimilar metal corrosion is classified as electrochemical attack and can remain undetected until structural failure occurs.
Cleaning Challenges and Corrosion Types
- Improper use of steel cleaning products can introduce small steel particles that cause corrosion.
- Intergranular corrosion affects grain boundaries in alloys and is caused by alloy structure inconsistencies.
- Aluminum alloys and some steels are particularly vulnerable to intergranular corrosion.
- Exfoliation corrosion is an advanced intergranular type that lifts surface metal grains due to expanding corrosion products.
- Fretting corrosion occurs when two stationary surfaces experience slight relative movement, characterized by surface pitting and debris generation.
Preventive Maintenance and Best Practices
- Preventive maintenance for corrosion resistance includes material improvements, surface treatments, insulation, and advanced protective finishes.
- Key corrosion PM functions:
- Regular cleaning and lubrication.
- Detailed corrosion inspections and protective system checks.
- Prompt treatment of corrosion and paint touch-ups.
- Accurate record-keeping and reporting of deficiencies.
- Use of suitable materials, tools, publications, and properly trained personnel.
- Maintenance of basic finish systems and keeping drainage paths clear.
- Daily draining of fuel cell sumps and cleaning of exposed critical areas.
- Sealing aircraft against water during poor weather and ensuring ventilation on sunny days.
- Replacing damaged gaskets and sealants to thwart water intrusion and entrapment.
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Description
Test your knowledge on Chapter 8 of the corrosion control textbook, focusing on cleaning and corrosion specific to aircraft. This quiz covers key references like FAA Advisory Circular 43-4B and the types of corrosion affecting aluminum and magnesium. Prepare to enhance your understanding of corrosion management in aviation.